# A Classical Introduction to Cryptography Exercise BookFrom Cryptography to Communication Security

A Classical Introduction to Cryptography Exercise Book: From Cryptography to Communication Security Chapter 12 FROM CRYPTOGRAPHY TO COMMUNICATION SECURITY Exercises Exercise 1 A Hybrid Cryptosystem Using RSA and DES The boss of a small company wants to secure all digital exchanges among the computers of the employees. As he is stingy, he does not want to hire a cryptographer and decides to set up a complete system by himself (he borrowed a textbook in the library). More precisely, he wants to use RSA and DES in order to build a hybrid cryptosystem. Such a scheme assumes that each employee of the company has a private key and that the associated public key is known to all the other employees. Figure 12.1 illustrates an example of the setup of a secure communication between Alice and Bob (two employees of the company). The principle is first, to establish a DES secret key (the session key) to be used in a session, second, to encrypt every message of the session with this session key. We denote by (nA, eA) and (nB, eB) the RSA public keys of Alice and Bob respectively, and by dA and dB the corresponding private keys. The session key will simply be denoted k. As the boss of the company http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png

# A Classical Introduction to Cryptography Exercise BookFrom Cryptography to Communication Security

17 pages

/lp/springer-journals/a-classical-introduction-to-cryptography-exercise-book-from-R4yVKA8DOG
Publisher
Springer US
ISBN
978-0-387-27934-3
Pages
231 –248
DOI
10.1007/0-387-28835-X_12
Publisher site
See Chapter on Publisher Site

### Abstract

Chapter 12 FROM CRYPTOGRAPHY TO COMMUNICATION SECURITY Exercises Exercise 1 A Hybrid Cryptosystem Using RSA and DES The boss of a small company wants to secure all digital exchanges among the computers of the employees. As he is stingy, he does not want to hire a cryptographer and decides to set up a complete system by himself (he borrowed a textbook in the library). More precisely, he wants to use RSA and DES in order to build a hybrid cryptosystem. Such a scheme assumes that each employee of the company has a private key and that the associated public key is known to all the other employees. Figure 12.1 illustrates an example of the setup of a secure communication between Alice and Bob (two employees of the company). The principle is first, to establish a DES secret key (the session key) to be used in a session, second, to encrypt every message of the session with this session key. We denote by (nA, eA) and (nB, eB) the RSA public keys of Alice and Bob respectively, and by dA and dB the corresponding private keys. The session key will simply be denoted k. As the boss of the company

Published: Jan 1, 2006

Keywords: Hash Function; Certificate Authority; Symmetric Encryption; Modular Exponentiation; Wired Equivalent Privacy